Variable-volume nozzle arrangement

ABSTRACT

A nozzle arrangement for an inkjet printhead includes a substrate assembly defining an ink inlet; a static ink ejecting member extending from the substrate assembly and bounding the ink inlet; an active ink ejecting member having a roof and sidewalls that depends from the roof towards the substrate, the roof defining an ink ejection port and the active ink ejecting member movably located relative to the static ink ejecting member to define a variable-volume nozzle chamber; and an actuator arrangement configured to reciprocate the active ink ejection member relative to the static ink ejecting member to eject ink in the nozzle chamber out through the ink ejection port. The static ink ejecting member is located within bounds delimited by the sidewalls of the active ink ejecting member.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.12/276,359 filed on Nov. 23, 2008, now issued with U.S. Pat. No.7,571,988, which is a Continuation of U.S. application Ser. No.11/706,307 filed on Feb. 16, 2007, now granted U.S. Pat. No. 7,465,025,which is a Continuation of U.S. application Ser. No. 11/478,587 filed onJul. 3, 2006, now granted U.S. Pat. No. 7,201,472, which is aContinuation of U.S. application Ser. No. 11/144,758 filed on Jun. 6,2005, now granted U.S. Pat. No. 7,156,496, which is a Continuation ofU.S. application Ser. No. 10/636,205 filed on Aug. 8, 2003, now grantedU.S. Pat. No. 6,921,153, which is a Continuation-In-Part of U.S.application Ser. No. 09/575,152 filed on May 23, 2000, now granted U.S.Pat. No. 7,018,016, all of which is herein incorporated by reference.

REFERENCED PATENT APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 09/575,152. The following applications and patentsare hereby incorporated by reference:

6,428,133 6,526,658 6,315,399 6,338,548 6,540,319 6,328,431 6,328,4256,991,320 6,383,833 6,464,332 6,390,591 7,018,016 6,328,417 6,322,1946,382,779 6,629,745 09/575,197 7,079,712 6,825,945 7,330,974 6,813,0396,987,506 7,038,797 6,980,318 6,816,274 7,102,772 7,350,236 6,681,0456,728,000 7,173,722 7,088,459 09/575,181 7,068,382 7,062,651 6,789,1946,789,191 6,644,642 6,502,614 6,622,999 6,669,385 6,549,935 6,987,5736,727,996 6,591,884 6,439,706 6,760,119 7,295,332 6,290,349 6,428,1556,785,016 6,870,966 6,822,639 6,737,591 7,055,739 7,233,320 6,830,1966,832,717 6,957,768 7,456,820 7,170,499 7,106,888 7,123,239 6,409,3236,281,912 6,604,810 6,318,920 6,488,422 6,795,215 7,154,638 6,924,9076,712,452 6,416,160 6,238,043 6,958,826 6,812,972 6,553,459 6,967,7416,956,669 6,903,766 6,804,026 7,259,889 6,975,429 6,485,123 6,425,6576,488,358 7,021,746 6,712,986 6,981,757 6,505,912 6,439,694 6,364,4616,378,990 6,425,658 6,488,361 6,814,429 6,471,336 6,457,813 6,540,3316,454,396 6,464,325 6,443,559 6,435,664 6,488,360 6,550,896 6,439,6956,447,100 7,381,340 6,488,359 6,618,117 6,803,989 7,044,589 6,416,1546,547,364 6,644,771 6,565,181 6,857,719 6,702,417 6,918,654 6,616,2716,623,108 6,625,874 6,547,368 6,508,546

FIELD OF THE INVENTION

This invention relates to a fluidic sealing structure. Moreparticularly, this invention relates to a liquid displacement assemblythat incorporates a fluidic seal.

BACKGROUND OF THE INVENTION

As set out in the above referenced applications/patents, the Applicanthas spent a substantial amount of time and effort in developingprintheads that incorporate micro electro-mechanical system (MEMS)-basedcomponents to achieve the ejection of ink necessary for printing.

As a result of the Applicant's research and development, the Applicanthas been able to develop printheads having one or more printhead chipsthat together incorporate up to 84 000 nozzle arrangements. TheApplicant has also developed suitable processor technology that iscapable of controlling operation of such printheads. In particular, theprocessor technology and the printheads are capable of cooperating togenerate resolutions of 1600 dpi and higher in some cases. Examples ofsuitable processor technology are provided in the above referencedpatent applications/patents.

The Applicant has overcome substantial difficulties in achieving thenecessary ink flow and ink drop separation within the ink jetprintheads.

Each of the nozzle arrangements of the printhead chip incorporates oneor more moving components in order to achieve drop ejection. The movingcomponents are provided in a number of various configurations.

Generally, each nozzle arrangement has a structure that at leastpartially defines a nozzle chamber. This structure can be active orstatic.

When the structure is active, the structure moves relative to a chipsubstrate to eject ink from an ink ejection port defined by thestructure. In this configuration, the structure can define just a rooffor the nozzle chamber or can define both the roof and sidewalls of thenozzle chamber. Further, in this configuration, a static ink ejectionformation is provided. The active structure moves relative to thisformation to reduce a volume of the nozzle chamber in order to achievethe necessary build up of ink pressure. The static formation can simplybe walls defined by the substrate. In this case, the active structure isusually in the form of a roof that is displaceable into and out of thenozzle chamber to achieve the ejection of ink from the ink ejectionport.

Instead, the static formation can extend into the nozzle chamber todefine an ink ejection area that faces a direction of ink drop ejection.The active structure then includes sidewalls that move relative to thestatic formation when the active structure is displaced to eject ink.

It will be appreciated that some form of seal is required between theactive structure and the static formation to inhibit ink from escapingfrom the nozzle chamber when the active structure is displaced towardsthe substrate and ink pressure is developed in the nozzle chamber.

When the structure defining the nozzle chamber is static, an inkejection member is usually positioned in the nozzle chamber. Thestructure also has a roof with an ink ejection port defined in the roof.The ink ejection member is often connected to an actuator that extendsthrough a wall of the structure. The ink ejection member is actuated bythe actuator to be displaceable towards and away from the roof to ejectink from the ink ejection port.

It will be appreciated that a seal is required at a juncture between theactuator or ink ejection member and the wall.

Applicant has found that it is convenient to use a surface tension ofthe ink to set up a fluidic seal between the active and staticcomponents of the nozzle arrangements. The fluidic seal uses surfacetension of the ink to set up a meniscus between the active and staticcomponents so that the meniscus can act as a suitable seal to inhibitthe leakage of ink.

Cohesive forces between liquid molecules are responsible for thephenomenon known as surface tension. The molecules at the surface do nothave other like molecules on all sides of them and consequently theycohere more strongly to those directly associated with them on thesurface. This forms a surface “film” which makes it more difficult tomove an object through the surface than to move it when it is completelysubmersed.

Surface tension is typically measured in dynes/cm, the force in dynesrequired to break a film of length 1 cm. Equivalently, it can be statedas surface energy in ergs per square centimeter. Water at 20° C. has asurface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and465 for mercury.

As is also known, a liquid can also experience adhesive forces when themolecules adhere to a material other than the liquid. This causes suchphenomena as capillary action.

Applicant has found that an effective fluidic seal can be achieved byutilizing the phenomena of surface tension and adhesion.

A particular difficulty that the Applicant has discovered and addressedin achieving such a fluidic seal is the problem associated withexcessive adhesion or “wetting” when a meniscus is stretched toaccommodate relative movement of the active and static components. Inparticular, wetting occurs when the relative movement overcomes surfacetension and an edge of the meniscus moves across a surface, to which themeniscus is adhered. This results in a weakening of the meniscus due tothe larger area of the meniscus and increases the likelihood of failureof the meniscus and subsequent leaking of ink.

The Applicant has conceived this invention in order to address thesedifficulties. Furthermore, the Applicant has obtained surprisinglyeffective fluidic seals when addressing these difficulties by developingsealing structures that support such fluidic seals.

SUMMARY OF THE INVENTION

A nozzle arrangement for an inkjet printhead includes a substrateassembly defining an ink inlet; a static ink ejecting member extendingfrom the substrate assembly and bounding the ink inlet; an active inkejecting member having a roof and sidewalls that depends from the rooftowards the substrate, the roof defining an ink ejection port and theactive ink ejecting member movably located relative to the static inkejecting member to define a variable-volume nozzle chamber; and anactuator arrangement configured to reciprocate the active ink ejectionmember relative to the static ink ejecting member to eject ink in thenozzle chamber out through the ink ejection port. The static inkejecting member is located within bounds delimited by the sidewalls ofthe active ink ejecting member.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a schematic side view of a pair of sealing formations toindicate a disadvantage associated with such a configuration;

FIG. 2 shows a schematic side view of a pair of sealing formations of afirst embodiment of a liquid displacement assembly, in accordance withthe invention;

FIG. 3 shows a schematic side view of a pair of sealing formations of asecond embodiment of a liquid displacement assembly, in accordance withthe invention;

FIG. 4 shows a schematic side view of a pair of sealing formations of athird embodiment of a liquid displacement assembly, in accordance withthe invention;

FIG. 5 shows a schematic side view of a pair of sealing formations of afourth embodiment of a liquid displacement assembly, in accordance withthe invention;

FIG. 6 shows a schematic side view of a pair of sealing formations of afifth embodiment of a liquid displacement assembly, in accordance withthe invention;

FIG. 7 shows a schematic sectioned side view of a nozzle arrangement ofa first embodiment of a printhead chip, in accordance with theinvention, in a quiescent condition;

FIG. 8 shows a schematic sectioned side view of the nozzle arrangementof FIG. 7 in an operative condition;

FIG. 9 shows a plan sectioned view of the nozzle arrangement of FIG. 7,taken through IX-IX in FIG. 7; and

FIG. 10 shows a schematic sectioned side view of a nozzle arrangement ofa second embodiment of a printhead chip, in accordance with theinvention, in an operative condition.

DETAILED DESCRIPTION OF THE INVENTION

This invention is directed towards the use of surface tension in orderto provide a fluidic seal. Cohesive forces between liquid molecules areresponsible for the phenomenon known as surface tension. Liquidmolecules at a surface of a body of liquid do not have other likemolecules on all sides of them and consequently they cohere morestrongly to those directly associated with them on the surface. Thisforms a surface “film” which makes it more difficult to move an objectthrough the surface than to move it when it is completely submersed.Surface tension is typically measured in dynes/cm, the force in dynesrequired to break a film of length 1 cm. Equivalently, it can be statedas surface energy in ergs per square centimeter. Water at 20° C. has asurface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and465 for mercury.

Applicant has found that it is this surface tension is high enough incertain liquids to serve as a fluidic seal, provided that there aresuitable formations to support a meniscus carrying the surface tension.

Surface tension plays a role in what is known as capillarity. Thismanifests itself when the liquid of the meniscus “wets” a surfacesupporting the meniscus. Wetting occurs when a contact angle definedbetween an edge of the meniscus and the surface reaches zero degrees.This wetting results in adhesive forces being set up between the liquidmolecules and the molecules of the material defining the surface. Whenthe adhesive forces are greater than the cohesive forces defining thesurface tension, the edge of the meniscus is drawn along the surface,resulting in an increase in size of the meniscus. In water, for example,the adhesive forces between water molecules and the walls of a glasstube are stronger than the cohesive forces. Thus, the water can be drawnthrough such a tube against gravity, provided the tube is thin enough.

A fluidic seal is used when it is necessary to prevent liquid fromescaping between components that move relative to each other. Aparticular advantage of a fluidic seal is that it uses the properties ofthe liquid to achieve sealing. It follows that the need for specializedsealing materials is obviated. However, it is important thatdisplacement of edges of a meniscus defining the fluidic seal beconstrained. This displacement can result in an increase in meniscusarea. This increase also increases forces counteracting the surfacetension, resulting in a breakdown of the meniscus and subsequentleaking. The Applicant has noted that movement of an edge of a meniscuscan be substantially curtailed if the surface to which the edge isadhered is directed away from a direction of force exerted on themeniscus by such factors as gravity and liquid pressure.

In this description, a plane of reference, indicated by a reference line11 is shown in the drawings. This is merely for ease of description.Furthermore, for the sake of convenience, the plane of reference isassumed to be horizontal, regardless of the fact that, as a whole, thevarious embodiments shown can be in any number of different orientationswith respect to a true horizon. Still further, a direction towards theplane of reference 11 is assumed to be downward and a direction awayfrom the plane of reference is assumed to be upward.

An example of an unsuitable sealing structure is indicated by referencenumeral 10 in FIG. 1. The solid lines indicate the sealing structure 10in a quiescent condition, while the dotted lines indicate the sealingstructure 10 in an operative condition. In this example, a sidewall 12of an active liquid displacement member moves vertically relative to acomplementary sidewall 14 of a static liquid displacement member. Thepurpose for this displacement can be multifold. However, in thisexample, the purpose is for increasing and subsequently decreasingpressure of a liquid 16 positioned in a chamber, such as a nozzlechamber 18. The sidewall 12 is displaced towards and away from asubstrate 20 as indicated by an arrow 22.

As can be seen, the complementary sidewall 14 has a vertically extendingexternal surface 26. When the structure 10 is in a quiescent condition,a meniscus 24 is formed between a free edge 28 of the sidewall 12 andthe external surface 26. When the structure 10 moves into the operativecondition, a contact angle defined between the meniscus 24 and theexternal surface 26 reaches zero degrees, and the liquid 16 wets theexternal surface 26. As a result, the liquid 16 simply follows theexternal surface 26 towards the substrate 20 as shown by the dottedlines 30. The meniscus 24 then expands to an extent to which thecohesive forces are broken and the liquid 16 leaks from between thesidewalls 12, 14.

In FIGS. 2 to 6, there are shown various sealing structures that aresuitable, to a greater or lesser extent, for inhibiting leakage of theliquid. All these structures form part of respective liquid displacementassemblies that fall within the scope of this invention. It is to beunderstood that the principles elucidated by these examples areapplicable to a wide range of dimensions. The Applicant is presentlyinvolved in MEMS-based structures, and these examples are well suited tosuch structures. In the background to the invention it is set out thatthe Applicant has developed printhead technology in which up to 84 000nozzle arrangements are incorporated into a single printhead. Theprinthead can include one or more printhead chips that span a printmedium.

In accordance with this invention, each of the nozzle arrangements caninclude any of the sealing structures as shown in FIGS. 2 to 6. Itfollows that in this application, the sealing structures are on amicroscopic scale, with sidewalls having a thickness of only a fewmicrons. Further, a gap between the sidewalls is also only a few micronswide. It will be appreciated that such dimensions enhance the effects ofsurface tension. However, such small dimensions also enhance suchphenomena as capillarity. It follows that the sealing structures shouldbe dimensioned to inhibit excessive capillarity.

It is to be appreciated that, while the scale of the nozzle arrangementsdeveloped by the Applicant are microscopic, this invention findsapplication on the macroscopic scale as well. For example, with liquidsand materials having certain characteristics, it is possible that thesidewalls and a gap between the sidewall could be visible by the nakedeye. In other words, the sidewalls and the gap could have transversedimensions that are measured in millimeters and large fractions of amillimeter.

It is to be noted that the orientation of the structures in FIGS. 1 to 6is not intended to indicate their practical orientation in use. Itfollows that the effect of gravity should not be taken into account inthese examples.

As set out in the background, the MEMS-based printhead is the product ofan integrated circuit fabrication technique. Silicon dioxide is widelyused in such techniques. As is known, silicon dioxide is simply anextremely pure glass. It follows that in this application, the sidewalls12, 14 can be in the form of glass or a glass-like material.Furthermore, most inks are substantially water-based. It follows thatinteraction between the sidewalls 12, 14 and the liquid 16 can besimilar to an interaction between glass and water.

Thus, in the structure 10, since the liquid 16 is water-like and thesidewalls 12, 14 are of a glass-like material, capillarity will manifestitself between the sidewalls 12, 14 and could draw the liquid 16 outbetween the sidewalls 12, 14 so that leakage occurs between thesidewalls 12, 14. This is especially so when the sidewall 12 isdisplaced relative to the sidewall 14.

In FIG. 2, reference numeral 32 generally indicates a sealing structure,of a liquid displacement assembly, in accordance with the invention,that is suitable, under predetermined conditions, for setting up aneffective fluidic seal to inhibit such leaking. With reference to FIG.1, like reference numerals refer to like parts, unless otherwisespecified.

The structure 32 has a complementary sidewall 34. A sealing formation 36is positioned on the complementary sidewall 34. A first horizontalsection 38, a second vertically downward section 40 and a thirdhorizontal section 42 that extends towards the complementary sidewall 34define the sealing formation 36. Thus, the sealing formation 36 has are-entrant transverse profile.

In this example, the third horizontal section 42 defines a liquidadhesion surface 44. When the sealing structure 36 is in a quiescentcondition, a meniscus 46 is formed between the free edge 28 of thesidewall 12 and an outer edge 48 of the liquid adhesion surface 44. Asindicated by the dotted lines 50, when the sealing structure 36 movesinto an operative condition, the meniscus 46 is positioned between thefree edge 28 and an inner edge 52 of the liquid adhesion surface 44.Furthermore, since the surface 44 effectively turns upwardly and awayfrom the plane of reference 11, the meniscus 46 is unable to extend pastthe inner edge 52. This serves to inhibit excessive enlarging of themeniscus 46 and subsequent leaking in the manner described above.

In FIG. 3, reference numeral 54 generally indicates a sealing structure,of a liquid displacement assembly, in accordance with the invention,that is also suitable, under certain conditions, for setting up afluidic seal that inhibits such leaking. With reference to FIGS. 1 and2, like reference numerals refer to like parts, unless otherwisespecified.

The sealing structure 54 has a complementary sidewall 56. A sealingformation 58 is positioned on the complementary sidewall 56. The sealingformation 58 is in the form of an outwardly extending horizontal ledge60. The ledge 60 defines a horizontal liquid adhesion surface 62.

When the structure 54 is in a quiescent condition, a meniscus 64 isdefined between the free edge 28 of the sidewall 12 and an outer edge 66of the liquid adhesion surface 62. When the structure 54 is in anoperative condition, the meniscus 64 moves into the condition shown bydotted lines 68.

It will be appreciated that it is undesirable that the meniscus 64reaches the complementary sidewall 56, since this will result in wettingof the complementary sidewall 56 and subsequent leakage. A simple forceanalysis reveals that whether the meniscus 64 does reach thecomplementary sidewall 56 depends on a contact angle that is definedbetween the meniscus 64 and the complementary sidewall 56. This contactangle increases as the sidewall 12 moves downwardly and is dependent onthe extent of downward movement. It follows that the structure 54 isfunctional between certain ranges of movement of the sidewall 12.

In FIG. 4, reference numeral 70 generally indicates a sealing structure,of a liquid displacement assembly, in accordance with the invention,that is suitable, under certain conditions, for setting up a fluidicseal that inhibits leaking. With reference to FIGS. 1 to 3, likereference numerals refer to like parts, unless otherwise specified.

The sealing structure 70 includes a complementary sidewall 72. A sealingformation 74 is positioned on the sidewall 72. The sealing formation 74includes an outwardly and horizontally extending first section 76 and adownwardly extending vertical second section 78. The second sectionterminates facing the plane of reference 11. It follows that a free endof the sealing formation 74 defines a liquid adhesion surface 80. Italso follows that the sealing formation 74 has a re-entrant profile.

In this example, a meniscus 82 extends from the free edge 28 of thesidewall 12 to an outer edge 84 of the liquid adhesion surface 80, whenthe structure is in a quiescent condition. In the operative condition,the meniscus 82 extends from the free edge 28 to an inner edge 86 of thesurface 80 as indicated by dotted lines 88. In view of the precedingmaterial, it will be appreciated that an extent of movement of themeniscus 82 is dependent on a thickness of the second section 78.

As set out above, in MEMS-based devices, such as the nozzle arrangementdeveloped by the Applicant, the thickness of such a wall member is onlya few microns. It is therefore extremely difficult to use suchtechniques to achieve a liquid adhesion surface that is much narrowerthan a few microns, using conventional integrated circuit fabricationtechniques. Furthermore, the constraints on the extent of expansion ofthe meniscus 82 provided by the sealing structure 70 are sufficient toprovide a workable fluidic seal.

In FIG. 5, reference numeral 90 generally indicates an optimum sealingstructure, of a liquid displacement assembly, in accordance with theinvention. With reference to FIGS. 1 to 4, like reference numerals referto like parts, unless otherwise specified.

The sealing structure 90 is substantially the same as the sealingstructure 70, with the exception that a free end 92 of the sidewall 12is tapered to define a vertex. A free end 94 of the second section 78 isalso tapered to define a vertex.

In this optimum example, a meniscus 96 extends between the vertices 92,94. It will thus be appreciated that a surface area of the meniscus 96remains substantially unchanged as the structure 90 is displaced intoits operative condition, as indicated by dotted lines 98. The reason forthis is that the liquid adhesion surface defines by the vertices 92, 94is dimensioned on a molecular scale, thereby providing practically noscope for movement of an edge of the meniscus 96.

While the structure 90 is optimum, it is extremely difficult to achievethe structure 90 with conventional integrated circuit fabricationtechniques, as set out above. As is known, integrated circuitfabrication techniques involve deposition and subsequent etching ofvarious layers of material. As such, tapered forms, such as those of thestructure 90 are not practical and are extremely difficult and expensiveto achieve.

In FIG. 6, reference numeral 100 generally indicates a sealingstructure, of a liquid displacement assembly, in accordance with theinvention, that is suitable, under certain conditions, for setting up afluidic seal. With reference to FIGS. 1 to 5, like reference numeralsrefer to like parts, unless otherwise specified.

The structure 100 is substantially the same as the structure 70.However, a lip 102 is positioned on the second section 78 so that thelip 102 and the free end of the second section 78 define a liquidadhesion surface 104. The lip 102 is a structural requirement that isdetermined by required alignment accuracy in a stepper process used inthe fabrication of the sealing structure 100.

In this example, a meniscus 106 is set up between the free edge 28 ofthe sidewall 12 and an outer edge 108 of the lip 102 and the surface 104when the structure is in a quiescent condition. The meniscus 106 extendsfrom the free edge 28 of the sidewall 12 and an inner edge 110 of thesurface 104.

The lip 102 does serve to increase the area of the surface 104 over thearea of the surface 80. As set out above, this could be undesirable.However, the lip 102 is required for the stepper alignment processmentioned above and its exclusion could lead to fabrication errors thatwould outweigh any advantages that may be achieved by excluding the lip102.

In FIGS. 7 and 8, reference numeral 120 generally indicates a nozzlearrangement of a first embodiment of a printhead chip, in accordancewith the invention, for an ink jet printhead. With reference to FIGS. 1to 6, like reference numerals refer to like parts, unless otherwisespecified.

The nozzle arrangement 120 is one of a plurality of such nozzlearrangements positioned on a substrate 122 to define the printhead chipof the invention. As set out in the background, an ink jet printheaddeveloped by the Applicant can include up to 84 000 such nozzlearrangements. It follows that it is for the purposes of convenience andease of description that only one nozzle arrangement is shown. Inintegrated circuit fabrication techniques, it is usual practice toreplicate a large number of identical components on a single substratethat is subsequently diced into separate components. It follows that thereplication of the nozzle arrangement 120 to define the printhead chipshould be readily understood by a reader of ordinary skill in the art.

In the description that follows the substrate 122 is to be understood todefine the plane of reference 11 used in the preceding description. Itfollows that the same orientation naming conventions apply in thefollowing description.

In FIG. 7, the nozzle arrangement 120 is shown in a quiescent conditionand in FIG. 8, the nozzle arrangement 120 is shown in an operativecondition.

An ink inlet channel 128 is defined through the substrate 122 to be influid communication with an ink inlet opening 130.

The nozzle arrangement 120 includes a static ink ejecting member 124 andan active ink ejecting member 126. The static ink ejecting member 124has a wall portion 136 that is positioned on the substrate 122 to boundthe ink inlet opening 130. The active ink ejecting member 126 includes aroof 132 and a sidewall 134 that depends from the roof 132 towards thesubstrate 122. The sidewall 134 is positioned outside of the wallportion 136, so that the sidewall 134 and the wall portion 136 define anozzle chamber 138.

An ink ejection port 140 is defined in the roof 132 and is aligned withthe ink inlet opening 130.

The wall portion 136 includes a sidewall 142 that extends from thesubstrate 122 towards the roof 132. A ledge 144 is positioned on thesidewall 142 and extends horizontally towards a position above the inkinlet opening 130. A sealing formation 146 is also positioned on thesidewall 142 and extends outwardly from the sidewall 142.

The sidewall 134 has a free end 148 that has a rectangular transverseprofile. The sealing formation 146 has a horizontal first section 150that extends from an upper end of the sidewall 142. A vertical secondsection 152 extends downwardly from an end of the first section 150. Alip 154 extends horizontally and outwardly from the second section 152.It follows that the sealing formation 146 is the same as the sealingformation 74 of the sealing structure 100 shown in FIG. 6. Further, thesidewall 134 is positioned relative to the sealing formation 146 so thatthe sidewall 134 and the sealing formation 146 define a sealingstructure 156 that is substantially the same as the sealing structure100. It follows that the lip 154 and the vertical second section 152define an ink adhesion surface 158.

As can be seen in FIGS. 7 and 8, a meniscus 160 is formed between thefree end 148 of the sidewall 134 and the ink adhesion surface 158 whenthe nozzle chamber 138 is filled with ink 162. Thus, a fluidic seal isset up between the sealing structure 156 and the sidewall 134. Theoperation and purpose of this fluidic seal has been fully describedearlier in this description. As can be seen in the drawings, the roof132 and sidewall 134 are displaced vertically downwardly towards thesubstrate so that an ink drop 164 is formed outside of the ink ejectionport 140. During this displacement, an edge of the meniscus 160 movesfrom one side of the ink adhesion surface 158 to an opposed side toaccommodate this movement. When the roof 132 and the sidewall 134 moveback into the position shown in FIG. 7, the ink drop 164 separates fromthe remainder of the ink 162 in the nozzle chamber 138.

The sealing structure 156 and the ledge 144 have a vertically facingsurface area that is sufficient to facilitate the ejection of ink, asdescribed above, when the roof 132 is displaced towards the substrate122.

The nozzle arrangement 120 includes a pair of symmetrically opposedthermal actuators 166 that act on the roof 132 to eject the ink drop164. Each thermal actuator 166 is connected to suitable drive circuitry(not shown) arranged on the substrate 122. Details of the thermalactuators are set out in the above referenced applications and aretherefore not set out in this description.

Each thermal actuator 166 is in the form of a bend actuator. It followsthat a suitable connecting structure 168 is positioned intermediate eachthermal actuator 166 and the roof 132. The connecting structures areconfigured to accommodate the different forms of movement of the roof132 and the actuators 166. Further details of these connectingstructures 168 are provided in the above referenced applications and aretherefore not set out here.

In FIG. 10, reference numeral 170 generally indicates a nozzlearrangement of a second embodiment of a printhead chip, in accordancewith the invention. With reference to FIGS. 1 to 9, like referencenumerals refer to like parts, unless otherwise specified.

As with the nozzle arrangement 120, the nozzle arrangement 170 is one ofa plurality of such nozzle arrangements set out on a substrate 172 todefine the printhead chip of the invention. The reasoning behind this asbeen set out above and applies here as well. As with the previousembodiment, the substrate 172 is assumed, for the purposes ofconvenience, to define the plane of reference 11 referred to earlier inthis description. Thus, the orientation terminology referred to earlieris used in the following description.

A sidewall 174 and a roof 176 are positioned on the substrate 172 todefine a nozzle chamber 178. An ink ejection port 180 is defined in theroof 176.

The substrate 172 includes silicon wafer substrate 184, a CMOS layer 186that defines drive circuitry for the nozzle arrangement 170 and an inkpassivation layer 188 positioned on the CMOS layer 186.

An ink ejection member in the form of a paddle 182 is positioned in thenozzle chamber 178. The paddle 182 is connected to a thermal bendactuator 190 with a connecting member 192 interposed between the paddle182 and the thermal bend actuator 190.

The thermal bend actuator 190 is connected to the CMOS layer 186 withsuitable vias 194 so that the thermal bend actuator 190 can be driven bythe drive circuitry. The thermal bend actuator 190 and its operation arefully described in the above referenced applications and these detailsare therefore not set out here. The thermal bend actuator 190 serves todisplace the paddle 182 through an arc towards and away from the inkejection port 180. In FIG. 10, the nozzle arrangement 170 is shown in anoperative position with the paddle 182 displaced towards the inkejection port 180 so that ink 196 within the nozzle chamber 178 isejected from the ink ejection port 180 to form a drop 198. The drop 198separates from the ink 196 when the paddle 182 returns to a quiescentcondition and ink pressure in the nozzle chamber 178 drops. The nozzlechamber 178 is in fluid communication with an ink inlet channel 200defined in the substrate 172, so that the nozzle chamber 178 can berefilled with ink once the drop 198 has been ejected. This occurs whenthe pressure drop mentioned above is equalized.

The connecting member 192 and roof 176 define an upper sealing structure202. The connecting member 192 and the sidewall 174 define a lowersealing structure 204.

The upper sealing structure 202 includes a sealing formation in the formof an outer, elongate plate 206 positioned on an inner side 208 of theconnecting member 192 adjacent an upper surface 210 of the connectingmember 192. When the nozzle arrangement 170 is in a quiescent condition,the plate 206 is positioned in a vertical plane.

The upper sealing structure 202 includes a further sealing formation inthe form of an inner, elongate plate 212 that is positioned on the roof176. The inner elongate plate 212 is horizontally aligned with the outerplate 206, when the nozzle arrangement 170 is in a quiescent condition.Further, a gap 214 defined between the plates 206, 212 is such that ameniscus 216 is formed between the plates 206, 212, the meniscus 216extending between upper edges 218, 220 of the plates 206, 212,respectively.

The edges 218, 220 are proud of the surface 210 and the roof 176,respectively. Thus, an extent of movement of edges of the meniscus 216is determined by a thickness of the plates 206, 212. It follows thatwhen the paddle 182 is displaced towards and away from the ink ejectionport 180, as described above, the meniscus 216 defines a fluidic seal toinhibit leaking of the ink 196. As set out above, the reason behind thisis that a contact angle of the meniscus 216 with the plates 206, 212does not reach zero degrees during movement of the connecting member 192relative to the roof 176.

The lower sealing structure 204 includes a lower sealing formation inthe form of a downward projection 222 defined by the connecting member192. The sidewall 174 defines a sealing formation in the form of are-entrant wall portion 224 positioned on the substrate 172. There-entrant wall portion 224 includes an outer rim 226 that ishorizontally aligned with the downward projection 222 when the nozzlearrangement 170 is in a quiescent condition. A meniscus 228 extendsbetween the downward projection 222 and the outer rim 226 when thenozzle chamber 178 is filled with the ink 196.

As is clear from the drawings, the sealing structure 204 is similar inform to the sealing structures 70 and 90 shown in FIGS. 4 and 5respectively. The operation and advantages of the sealing structure 204are therefore clear and need not be described at this stage. It followsthat the meniscus 228 defines a suitable fluidic seal that inhibits theleaking of ink during operation of the nozzle arrangement 170.

1. A nozzle arrangement for an inkjet printhead, the nozzle arrangementcomprising: a substrate assembly defining an ink inlet; a static inkejecting member extending from the substrate assembly and bounding theink inlet; an active ink ejecting member having a roof and sidewallsthat depends from the roof towards the substrate, the roof defining anink ejection port and the active ink ejecting member movably locatedrelative to the static ink ejecting member to define a variable-volumenozzle chamber; and an actuator arrangement configured to reciprocatethe active ink ejection member relative to the static ink ejectingmember to eject ink in the nozzle chamber out through the ink ejectionport, wherein the static ink ejecting member is located within boundsdelimited by the sidewalls of the active ink ejecting member andincludes a sealing formation extending towards the sidewalls, thesealing formation for forming a fluidic seal with the sidewall, and thesealing formation is provided at an upper edge of the static inkejecting member, and shaped to extend outwards and downwards withrespect to the upper edge of the static ink ejecting member.
 2. A nozzlearrangement as claimed in claim 1, wherein ink ejection port is alignedwith the ink inlet.
 3. A nozzle arrangement as claimed in claim 1,wherein the static ink ejecting member includes a ledge that extendshorizontally towards a position above the ink inlet.
 4. A nozzlearrangement as claimed in claim 1, wherein the actuator arrangementincludes a pair of symmetrically opposed thermal actuators that act onthe roof to eject the ink, each thermal actuator being connected todrive circuitry of the substrate assembly.
 5. A nozzle arrangement asclaimed in claim 4, wherein each thermal actuator is in the form of abend actuator and a connecting structure is positioned intermediate eachthermal actuator and the roof.